The measurement and prediction of soil erosion is important for understanding both natural and disturbed landscape systems. In particular numerical models of soil erosion are important tools for managing landscapes as well as understanding how they have evolved over time. Over the last 40 years a variety of methods have been used to determine rates of soil loss from a landscape and these can be loosely categorised into empirical and physically based models. Alternatively, physically based Landscape Evolution Models (LEM) have been developed that provide information on soil erosion rates at much longer decadal or centennial scales, over large spatial scales and examine how they may respond to environmental and climatic changes. Both soil erosion LEM's are interested in similar outcomes (landscape development and sediment delivery) yet have quite different methodologies and parameterisations. This paper applies a LEM (the CAESAR model) for the first time at time and space scales where soil erosion models have largely been used. It tests the LEM's ability to predict soil erosion on a 30 m experimental plot on a trial rehabilitated landform in the Northern Territory, Australia. It then continues to discuss the synergies and differences between soil erosion and landscape evolution models.

The results demonstrate that once calibrated for the site hydrology, predicted suspended sediment and bedload yields from CAESAR show a close correspondence in both volume and timing of field measured data. The model also predicts, at decadal scales, sediment loads close to that of field measured data. Findings indicate that the small scale drainage network that forms within these erosion plots is an important control on the timing and magnitude of sediment delivery. Therefore, it is important to use models that can alter the DEM to reflect changing topography and drainage network as well as having a greater emphasis on channel processes. Copyright © 2012 John Wiley & Sons, Ltd.

This paper examines the weathering processes that have combined to produce the distribution of soil-regolith (SR) thickness across the Triassic Sherwood Sandstone Group outcrop (750 km²) in Nottinghamshire, U.K. Archive borehole logs (n = 282) taken across the outcrop showed that soil-regolith thickness had mean and median depths of ~1.8 and 1.5 m respectively. Cores were taken from a forested site to depths ~3 m for geochemical analysis. At this site the SR thickness was ~1.7 m. Analysis of the loss of elements, compared to bedrock using mass balance calculations (τ) showed that all the calcite and gypsum cement had been removed to depths of >3 m. Thus the major difference between the SR and the underlying saprolite was that the former exists as loose sand as opposed to a semi-durable rock. Scanning electron microscopy (SEM) analysis of core samples suggested that the non-durable rock or saprolite had greater cementation of clay particles. We propose that the mechanism through which the clay cement (and other interlocking grain bonds) were eased apart was through freeze-thaw processes associated with the summer ‘active layer development’ during the last glacial activity in the UK. We tested this theory by developing a Monte Carlo simulation based on a simplified version of the Stefan Equation. Current Arctic datasets of air and ground temperatures were obtained to provide reasonable starting conditions for input variables. These were combined with known data for thermal conductivity, bulk density and moisture content of the Sherwood Sandstone regolith. Model predictions (n = 1000) of the distribution of SR thickness accurately reflect the observed distribution thickness from the borehole logs. This is strong evidence that freeze-thaw and ‘ALD’ processes are major factors in determining the thickness of SR across this outcrop. Copyright © 2012 British Geological Survey and John Wiley & Sons, Ltd.

Soils release more carbon, primarily as carbon dioxide, per annum than current global anthropogenic emissions (Luo and Zhou, 2006). Soils emit carbon dioxide through mineralization and decomposition of organic matter and respiration of roots and soil organisms (Houghton, 2007). Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO₂ emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO₂ emission, however, none examine their relative importance. Therefore, this study investigated the effects of soil compaction and exposure of the soil surface to rainfall and their interaction on CO₂ release. We conducted a factorial laboratory experiment with three soil types after sieving(clay, silt and sand soil), three different bulk densities (1.1 g cm^-3, 1.3 g cm^-3, 1.5 g cm^-3) and three different exposures to rainfall (no rain, 30 minutes and 90 minutes of rainfall). The results demonstrated CO₂ release varied significantly with bulk density, exposure to rain and time. The relationship between rain exposure and CO₂ is positive: CO₂ emission was 53% and 42% greater for the 90 minutes and 30 minutes rainfall exposure, respectively, compared to those not exposed to rain. Bulk density exhibited a negative relationship with CO₂ emission: soil compacted to a bulk density of 1.1 g cm^-3 emitted 32% more CO₂ than soil compacted to 1.5 g cm^-3. Furthermore we found that the magnitude of CO₂ effluxes depended on the interaction of these two abiotic factors. Given these results, understanding the influence of soil compaction and raindrop impact on CO₂ emission could lead to modified soil management practices which promote carbon sequestration. Copyright © 2012 John Wiley & Sons, Ltd.

In the Erlenbach stream, a pre-alpine steep channel in Switzerland, sediment transport has been monitored for more than 25 years. Near the confluence with the main valley river, stream flow is monitored and sediment is collected in a retention basin with a capacity of about 2,000 m³. The basin is surveyed at regular intervals and after large flood events. In addition, sediment transport has been continuously monitored with piezoelectric bedload impact and geophone sensors since 1986. In 2008–2009, the measuring system in the Erlenbach stream was enhanced by installing an automatic system to obtain bedload samples. Movable metal baskets are mounted on a rail at the downstream wall of the large check dam above the retention basin, and they can be moved automatically into the flow to take bedload transport samples. The wire mesh of the baskets has a spacing of 10 mm to sample all sediment particles coarser than this size (which is about the limiting grain size detected by the geophones). The upgraded measuring system permits to obtain bedload samples over short sampling periods and to measure the grain size distribution of the transported material and its variation over time and with discharge. The analysis of calibration relationships for the geophone measuring system confirms findings from very similar measurements which were performed until 1999 with piezoelectric bedload impact sensors; there is a linear relationship between impulse counts and bedload mass passing over the sensors. Findings from flume experiments are used to discuss the most important factors which affect the calibration of the geophone signal. The bedload transport rates as measured by the moving baskets are among the highest measured in natural streams, with values of the order of several kg/(m s). Copyright © 2012 John Wiley & Sons, Ltd.

The Wind Erosion Prediction System (WEPS) and Revised Wind Erosion Equation (RWEQ) are widely used for estimating wind-induced soil erosion at a field scale. Wind is the principal erosion driver in the two models. Wind erosivity, which describes the capacity of wind to cause soil erosion, is defined as erosive wind power density (WPD) in WEPS, and wind value (W) in RWEQ. In this study, the daily average WPD (AWPD) and the daily average W (Wf) were chosen to investigate the effect of averaging time on wind erosivity estimation based on observed wind data. We compare the daily AWPD and Wf calculated from 1, 5, 10, 15, 30, and 60 min average wind speed data.

The results of comparisons indicate that averaging wind speed can significantly influence estimates of wind erosivity. Compared with the daily AWPD and Wf calculated from 1 min average wind speed data, all daily AWPD and Wf values calculated from 5, 10, 15, 30, and 60 min averaged wind speeds tend to be significantly lower than values calculated from 1 min values. In general, longer averaging times tend to produce smaller values of daily AWPD or Wf, which may lead to an under-estimation of wind erosion. Further studies are needed to extend and apply the findings obtained in this study to actual wind erosion predictions. Copyright © 2012 John Wiley & Sons, Ltd.

Wildfires in the sub-alpine belt of the Austrian Limestone Alps sometimes cause severe vegetation and soil destruction with increased danger of secondary natural hazards such as avalanches and debris flows. Some of the affected areas remain degraded to rocky slopes even decades after the fire, raising the question as to whether the ecosystems will ever be able to recover. The mean fire interval, the duration of recovery and the role of geomorphic processes for vegetation regeneration are so far unknown. These questions were tackled in a broad research approach including investigation of historical archives to determine the frequency of historical wildfires, mapping vegetation regeneration on 20 slopes of different post-fire ages, and soil erosion measurements on two slopes. To date, >450 historical wildfires have been located in the study area. The mean fire interval per km² is c. 750 years, but can be as low as 200–500 years on south-facing slopes. Vegetation regeneration takes an extremely long time under unfavourable conditions; the typical window of disturbance is between 50 and 500 years, which is far longer than in any other wildfire study known to us. Soil erosion constantly increases in the years after the fires and the elevated intensity can be maintained for decades. A two-part vegetation regeneration model is proposed depending upon the degree of soil loss. In the case of moderate soil erosion, spreading grassland communities can slow down shrub recolonisation. In contrast, after severe soil destruction the slopes may remain degraded for a century or longer, before rather rapid regeneration occurs. The reasons are not fully understood but are probably governed by geomorphic process intensity. The interdependence of vegetation regeneration and geomorphic processes is a paradigm of ecology-geomorphology interaction, and is a unique example of a very long-lasting disturbance response caused by wildfire in a non-resilient ecosystem. Copyright © 2012 John Wiley & Sons, Ltd.

Many beaver ponds in the Rocky Mountains, that have been described in the literature, are in-channel ponds that are relatively small and short-lived. This paper describes floodplain beaver ponds on low-gradient deltas in glacial finger lakes in Glacier National Park, Montana. These ponds are distinctly larger, probably fed by hyporheic flow, and stable and long-lived. Ponds examined were, with one exception, 44 years old. Glacial discharge is present in each valley where beaver ponds occupy low-gradient deltas, and this discharge likely sustains pond water level over the course of the summer. As glaciers recede and disappear, deltaic beaver ponds dependent on hyporheic flow may be negatively affected. Copyright © 2012 John Wiley & Sons, Ltd.

Point measurements of flow rate, depth or velocity are not sufficient to validate overland flow models, particularly when the interaction of the water with the soil surface creates a complex flow geometry. In this study, we present the coupling of two techniques obtaining spatial data of flow depths and surface velocity measurements for water depths as low as a one millimetre. Overland flow experiments were performed in the laboratory at various flow rates and slopes on two surfaces. The first surface was 120 cm by 120 cm showing three undulations of sinusoidal shape with an amplitude of 1 cm and a wavelength of 20 cm, while the second was a 60 cm by 60 cm moulded reproduction of a seedbed with aggregates up to 2 cm in size. Large scale particle image velocimetry (LSPIV) was used for velocity measurements with a sub-centimetre spatial resolution. An instantaneous-profile laser scanner was used to map flow depths with a sub-millimetre spatial resolution. A sensitivity analysis of the image processing of the LSPIV showed a good robustness of the method. Comparison with measurements performed with hot film anemometer and salt velocity gauge showed that LSPIV surface velocities were representative of the flow. Water depths measured with the laser scanner were also in good agreement with single-point measurements performed with a dial indicator. Spatially-distributed flow rates could be computed by combining both presented techniques with a mean relative error less than 20%. Copyright © 2012 John Wiley & Sons, Ltd.

Knowledge of sediment exports from continental areas is essential for estimating denudation rates and biogeochemical cycles. However, the estimation of current sediment fluxes to the sea is often limited by the availability and quality of sediment discharge data. This study aims to quantify the relative contributions of French rivers to the sediment discharge to the ocean. Sediment fluxes were mainly assessed using the French river quality database, which is characterised by a low temporal resolution but long-term measurement periods. An improved rating curve approach (IRCA) using daily discharge data, which allows the estimation of mean annual sediment loads from infrequent sediment concentration data, was used to calculate sediment fluxes. The resulting mean annual sediment loads show that French rivers export ca. 18.91 Mt.yr^-1 of sediments to the sea. Among the 88 defined French rivers flowing to the sea, the four largest basins (Loire, Rhone, Garonne and Seine) export 15.8 Mt per year, which corresponds to 83.5% of total exports. No relationship was found between the mass of exported sediment and the size of the drainage basins. This is due to the variety of river basin typologies among these rivers, including lowland rivers in temperate climates, such as the Seine river on the one hand and rivers draining mountainous areas in Alpine/Mediterranean areas on the other hand, such as the Rhone river. The latter contributes 50% to the total sediment export for France while its drainage area is only 20% of the total area considered. Differences between the considered river basins are also shown by temporal indicators describing the duration of the exports, which may be linked with sediment production processes over drained areas. Copyright © 2012 John Wiley & Sons, Ltd.

In natural gravel-bed streams, the complex topography of the bed can cause variation of flow resistance and sediment transport. Previous studies have shown that in addition to grain resistance (skin friction), flow resistance is also caused by bank roughness, channel bars, bed undulations and channel curvature. Sediment transport is similarly influenced by the complex topography, and the transport rate can vary spatially. A 3D numerical models was used to generate a detailed description of the flow and bedload transport fields in gravel bed rivers. Here we quantify the reach-averaged hydraulic resistance and sediment transport regime that prevails when self-formed alternate river bars are present, and compare with the regime that would prevail were no bars are present. We do this by comparing the results of (a) a 3D morphodynamic model in which bars form as a consequence of flow-bed interaction and (b) an “equivalent” 1D case, which refers to flat bed conditions, but otherwise corresponding to identical average velocity and bed slope. The 3D numerical model is applied to generate different bed topographies of alternate bars at regime morphological equilibrium, then extended to non equilibrium conditions for decreasing shear stress within a sensitivity analysis context. The contribution of grain resistance is estimated with the local values of the bed shear stress, while bar resistance results from the overall deviation of the flow field from that occurring in the flat bed configuration. The local sediment transport in both the longitudinal and transverse directions is computed with the local Shields stress and local bed inclination. The calculations result in a method for correcting 1D models to account for the total sediment transport and resistance in a cross-section due to 3D effects of alternate bars. We term the resulting relations “morphologically averaged” sediment transport and resistance equations. Copyright © 2012 John Wiley & Sons, Ltd.

The lake levels in Lake Michigan-Huron have recently fallen to near historical lows, as has the elevation difference between Lake Michigan-Huron compared to Lake Erie. This decline in lake levels has the potential to cause detrimental impacts on the lake ecosystems, together with social and economic impacts on communities in the entire Great Lakes region. Results from past work suggest that morphological changes in the St. Clair River, which is the only natural outlet for Lake Michigan-Huron, could be an appreciable factor in the recent trends of lake level decline. A key research question is whether bed erosion within the river has caused an increase in water conveyance, therefore, contributed to the falling lake level. In this paper, a numerical modeling approach with field data is used to investigate the possibility of sediment movement in the St. Clair River and assess the likelihood of morphological change under the current flow regime. A two-dimensional numerical model was used to study flow structure, bed shear stress, and sediment mobility/armoring over a range of flow discharges. Boundary conditions for the numerical model were provided by detailed field measurements that included high-resolution bathymetry and three-dimensional flow velocities. The results indicate that, without considering other effects, under the current range of flow conditions, the shear stresses produced by the river flow are too low to transport most of the coarse bed sediment within the reach and are too low to cause substantial bed erosion or bed scour. However, the detailed maps of the bed show mobile bedforms in the upper St. Clair River that are indicative of sediment transport. Relatively high shear stresses near a constriction at the upstream end of the river and at channel bends could cause local scour and deposition. Ship-induced propeller wake erosion also is a likely cause of sediment movement in the entire reach. Other factors that may promote sediment movement, such as ice cover and dredging in the lower river, require further investigation. Copyright © 2012 John Wiley & Sons, Ltd.

Cracks are widely developed along the edge of loess platforms in NW China. Field surveys reveal that these cracks can be grouped into shallow and deeply penetrating ones. The former occur at a small distance from platform edge, normally penetrate into the top unsaturated loess with the penetration depth being controlled by the joints in loess. The latter penetrate deeper into the saturated loess farther away from the platform edge. These cracks control the inflow and drainage of irrigation water. The shallow penetrating crack can fail as a slide or fall with a volume of up to hundreds of cubic meters. The deeply penetrating crack can fail as a flow-like landslide with a volume of thousands of cubic meters or more. A full-scale field test simulating irrigation on the platform surface was conducted. The two types of crack can be interconnected so that the water applied in the test finally flowed into the deep crack and was discharged from the platform. Analysis of soil stress states and the results of field test show that the deeply-penetrating cracks could have both positive as well as negative effects on slope stability. On the one hand, water can flow more freely in the cracks, and the loess could be saturated and triggered landslide. On the other hand, the water can drain more easily along the crack and slope stability could be enhanced as the groundwater level is suppressed. Copyright © 2012 John Wiley & Sons, Ltd.

Northern rivers experience freeze-up over the winter, creating asymmetric under-ice flows. Field and laboratory measurements of under-ice flows typically exhibit flow asymmetry and its characteristics depend on the presence of roughness elements on the ice cover underside. In this study, flume experiments of flows under a simulated ice cover are presented. Open water conditions and simulated rough ice-covered flows are discussed. Mean flow and turbulent flow statistics were obtained from an Acoustic Doppler Velocimeter (ADV) above a gravel-bed surface. A central region of faster flow develops in the middle portion of the flow with the addition of a rough cover. The turbulent flow characteristics are unambiguously different when simulated ice covered conditions are used. Two distinct boundary layers (near the bed and in the vicinity of the ice cover, near the water surface) are clearly identified, each being characterized by high turbulent intensity levels. Detailed profile measurements of Reynolds stresses and turbulent kinetic energy indicate that the turbulence structure is strongly influenced by the presence of an ice cover and its roughness characteristics. In general, for y/d > 0.4 (where y is height above bed and d is local flow depth), the addition of cover and its roughening tends to generate higher turbulent kinetic energy values in comparison to open water flows and Reynolds stresses become increasingly negative due to increased turbulence levels in the vicinity of the rough ice cover. The high negative Reynolds stresses not only indicate high turbulence levels created by the rough ice cover but also coherent flow structures where quadrants 1 and 3 dominate. Copyright © 2012 John Wiley & Sons, Ltd.

Bedload transport is known to be a highly fluctuating temporal phenomenon, even under constant (mean) flow conditions, as a consequence of stochasticity, bedform migration, grain sorting, hysteresis, or sediment supply limitation. Because bedload transport formulas usually refer to a single mean transport value for a given flow condition, one can expect that prediction accuracy (when compared to measurements) will depend on the amplitude and duration of fluctuations, which in turn depend on the time scale used for observations. This paper aims to identify how the time scale considered can affect bedload prediction. This was done by testing 16 common bedload transport formulas with four data sets corresponding to different measurement period durations: (i) highly fluctuating (quasi-)instantaneous field measurements, (ii) volumes accumulated at the event scale on two small alpine gravel-bed rivers, potentially affected by seasonal fluctuations, (iii) volumes accumulated at the interannual scale in a meandering gravel bed river, thought to be weakly subject to fluctuations, and (iv) time-integrated flume measurements with nearly uniform sediments. The tests confirmed that the longer the measurement period, the better the precision of the formula's prediction interval. They also demonstrate several consequential limitations. Most threshold formulas are no longer valid when the flow condition is below two times the threshold condition for the largest elements’ motion on the bed surface (considering D₈₄). In such conditions, equations either predict zero transport, or largely overestimate the real transport, especially when D₈₄ is high. There is a need for new sediment data collected with highly reliable techniques such as recording slot bedload samplers to further investigate this topic. Copyright © 2012 John Wiley & Sons, Ltd.

Although volcanic eruptions are well-known to be the trigger of some weather and climatic changes, land-cover changes by pyroclastic-flows and lahars do not get this recognition, neither do major hazards such as tsunami. These two earth-processes are even lesser considered as being able to modify other earth-processes they are not directly connected to, such as landslides or river discharge in non-connected basins more than a hundred kilometers away. In this contribution the authors argue that these ideas are mainly driven by the process of being ‘educated’ in a single academic discipline and once put to the test interactions and retroactions between earth processes and atmospheric processes are far more reaching than commonly thought. For this study, the site of Java Island (Indonesia) was chosen to conduct (1) an analysis of a major tsunami impacts - in the same area than the 2006 Java tsunami -; and (2) an analysis of the post-eruption impacts of Merapi Volcano after a major eruption – excluding any ejecta in the atmosphere for the sake of the demonstration. The atmospheric feedback simulations were conducted using the Regional Climate Model (RegCM-4) with calibration from weather stations in Java Island. As a result, both simulations have proven that large scale deposits of pyroclasts (not introducing the ejectas sent in the atmosphere) and tsunamis can have outstanding impacts on the atmospheric situation and the bio-geomorphologic evolution of the landscape in the following weeks to months. Interestingly enough these impacts are not limited to the area impacted by the earth-process and the effect are not linear in time as they work following thresholds. These rainfalls ‘tele-impacts’ are important enough to, in turn, modify earth-surface processes in areas remote from the original pehonmenon. This system acts in the same manner than a famous butterfly in Africa that could trigger a hurricane on the other side of the Atlantic Ocean. Copyright © 2012 John Wiley & Sons, Ltd.

Applications of ergodic reasoning (or location for time substitution) aid efforts at environmental reconstruction and prediction, providing a useful tool to analyse and communicate stages of landscape evolution. Analysis of the historical range of behaviour and change that a river system has experienced can be used to interpret thresholds that have been breached, and underlying controls and/or triggers for adjustment and change. This information can be used to forecast future trajectories of adjustment and provide target conditions for management activities. This paper uses a case study from upper Wollombi Brook, New South Wales, Australia to demonstrate how ergodic reasoning can be used to assess river behaviour, change and responses to natural and human-disturbances. The ‘river evolution diagram’ developed by Brierley and Fryirs (2005) is presented as a means for depicting the range of behaviour and evolutionary variability of this river. These approaches can be readily applied in other systems. Implications for approaches to analysis of river evolution and management are outlined. Copyright © 2012 John Wiley & Sons, Ltd.

The San Antonio River Delta (SARD), Texas, has experienced two major avulsions in the past 80 years, and a number of other historical and Holocene channel shifts. The causes and consequences of these avulsions—one of which is ongoing—were examined using a combination of fieldwork, GIS analysis, and historical information to identify active, semiactive, and paleochannels and the sequence of shifting flow paths through the delta. The role of deposition patterns and antecedent morphology, large woody debris jams, and tectonic influences were given special attention. Sedimentation in the SARD is exacerbated by tectonic effects. Channel aggradation is ubiquitous, and superelevation of the channel bed above the level of backswamp areas on the floodplain is common. This creates ideal setup conditions for avulsions, and stable, cohesive fine-grained banks favor avulsions rather than lateral migration. Flood basins between the alluvial ridges associated with the aggraded channels exist, but avulsions occur by reoccupation of former channels found within or connected to the flood basins. Large woody debris and channel-blocking logjams are common, and sometimes displace flow from the channel, triggering crevasses. However, a large, recurring logjam at the site of the ongoing avulsion from the San Antonio River into Elm Bayou is not responsible for the channel shift. Rather, narrow, laterally stable channels resulting from flow splits lead to accumulation of wood. Some aspects of the SARD avulsion regime are typical of other deltas, while others are more novel. These includes avulsions involving tributaries and subchannels within the delta as well as from the dominant channel; tectonic influences on delta backstepping and on channel changes within the delta; avulsions as an indirect trigger for logjam formation (as well as vice-versa); and maintenance of a multi-channel flow pattern distinct from classic anastamosing or distributary systems. Copyright © 2012 John Wiley & Sons, Ltd.

Landscape evolution models (LEMs) simulate the three-dimensional development of landscapes over time. Different LEMs have different foci, e.g. erosional behaviour, river dynamics, the fluvial domain, hillslopes or a combination. LEM LAPSUS is a relatively simple cellular model operating on timescales of centuries to millennia and using annual timesteps that has had a hillslope focus. Our objective was to incorporate fluvial behaviour in LAPSUS without changing the existing model equations. The model should be able to reproduce alternating aggradation and incision in the floodplains of catchments, depending on simulated conditions. Testing was done using an artificial DEM and a demonstration of the ability for fluvial simulation was performed for a real landscape (Torrealvilla catchment, SE Spain).

Model equations to calculate sediment dynamics and water routing were similar for both hillslope and fluvial conditions, but different parameter values were used for these domains, defined based on annual discharge. Parameters changing between the domains are convergence factor p, which is used in the multiple flow algorithm to route water, and discharge and gradient exponents m and n, used in calculation of transport capacity.

Erodibility and ‘sedimentability’ factors K and P were changed between cold (little vegetation; high erodibility) and warm conditions (more vegetation, lower erodibility). Results show that the adapted parameters reproduced alternating aggradation - due to divergent flow in the floodplain and sediment supply under cold conditions - and incision due to reduced sediment supply and resulting clean water erosion during simulated warm conditions. The simulated results are due to interactions between hillslopes and floodplains, as the former provide the sediments that are deposited in the latter. Similar behaviour was demonstrated when using the real DEM. Sensitivity and resolution analysis showed that the model is sensitive to changes in m, n and p and that model behaviour is influenced by DEM resolution. Copyright © 2012 John Wiley & Sons, Ltd.

The evolution of a debris-flow cone depends on a multitude of factors in the hydrogeomorphic system. Investigations of debris-flow history and cone dynamics in highly active catchments therefore require an integrative approach with a temporal and spatial resolution appropriate for the goals of the study. We present the use of an orthophoto time series to augment standard dendrogeomorphic techniques to describe the spatio-temporal dynamics of debris flows on a highly active cone in the western Austrian Alps. Analysis of seven orthophotos since 1951 revealed a migration of active deposition areas with a resulting severe loss of forest cover (>80%) and a mean tree loss per year of 10.4 (range 1.3-16.6 trees per year). Analysis of 193 Pinus mugo ssp. uncinata trees allowed the identification of 161 growth disturbances corresponding to 16 debris flows since 1839 and an average decadal frequency of 0.9 events. As a result of the severe loss of forest cover, we speculate that <20% of the more recent events were actually captured in the tree-ring record, giving a decadal return interval of ~7.5 events for a period of 60 years. Based on three annual field observations, it is evident that this catchment (the Bärenrüfe) produces very frequent (<1 yr), small (in the order of a few 10 to 100 m³) debris flows with minor material relocation. The specific challenges of tree-ring analysis in this tree species and in highly active environments are explicitly addressed in the discussion and underline the necessity of employing complementary methods of analysis in an integrative manner. Copyright © 2012 John Wiley & Sons, Ltd.

Although the impact of sheet erosion on the evolution of soils, soil properties and associated ecosystem services across landscapes is undisputed, there are still large uncertainties in the estimation of sheet erosion, as the obtained results are highly scale-dependent. Consequently, there is a need to develop a scale explicit understanding of sediment erosion yields, from microplot to hillslope through to plot, to surmount actual erosion modelling flaws and to improve guidance for erosion mitigation. The main objective of this study was to compare sediment yields from small and large plots installed under different environmental conditions and to interpret these results in terms of the main mechanisms and controlling factors of sheet erosion. Fifteen 1 × 1 m² and ten 2 × 5 m² plots were installed on a hillslope in the foothills of the Drakensberg, South Africa. Data of runoff (R), sediment concentration (SC), soil loss (SL) and rainfall characteristics obtained during the 2009–2010 rainy season at the two spatial scales and from different soils, vegetation cover, geology and topographic conditions were used to identify the main controlling factors of sheet erosion. Scale ratios for SC and SL were subsequently calculated to access the level of contribution of rain-impacted flow (RIF) to overall sheet erosion. The average runoff rate (n = 17 events) ranged between 4.9 ± 0.4 L m^-2 on 1 m² and 5.4 ± 0.6 L m² on 10 m², which did not correspond to significant differences at p < 0.05 level. Sediment losses were significantly higher on the 10 m² plots, compared to the 1 m² plots (2.2 ± 0.4 vs 1.5 ± 0.2 g L^-1 for SC; 9.8 ± 1.8 vs 3.2 ± 0.3 g m^-2 for SL), which illustrated a greater efficiency of sheet erosion on longer slopes. Results from a principal component analysis, whose two first axes explained 60% of the data variance, suggested that sheet erosion is mainly controlled by rainfall characteristics (rainfall intensity and amount) and soil surface features (crusting and vegetation coverage). The contribution of RIF to sheet erosion was the lowest at high soil clay content (r = 0.26) and the highest at high soil bulk density (r = 0.22), cumulative rainfall amount in the season and associated rise in soil water table (r = 0.29). Such an explicit consideration of the role of scale on sediment yields and process domination by either in-situ (soil and soil surface conditions) or ex-situ (rainfall characteristics and antecedent rainfall) factors, is expected to contribute to process-based modelling and erosion mitigation. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents the predicted flow dynamics from the application of a Reynolds Averaged Navier Stokes model to a series of bifurcation geometries with morphologies measured during previous flume experiments. The topography of the bifurcations consists of either plane or bedform-dominated beds which may or may not possess discordance between the two bifurcation distributaries. Numerical predictions are compared with experimental results to assess the ability of the numerical model to reproduce the division of flow into the bifurcation distributaries. The hydrodynamic model predicts: 1) diverting fluxes in the upstream channel which direct water into the distributaries; 2) super-elevation of the free surface induced at the bifurcation edge by pressure differences; and 3) counter-rotating secondary circulation cells which develop upstream of the apex of the bifurcation and move into the downstream channels, with water converging at the surface and diverging at the bed. When bedforms are not present, weak transversal fluxes characterize the upstream channel for almost its entire length, associated with clearly distinguishable secondary circulation cells, although these may be under-estimated by the turbulence model used in the solution. In the bedform dominated case, the same hydrodynamic conditions were not observed, with the bifurcation influence restricted and depth scale secondary circulation cells not forming. The results also demonstrate that the dominant effect bed discordance has upon flow division between the two distributaries. Finally, results indicate that in bedform dominated rivers. Consequently, we suggest that sand-bed river bifurcations are more likely to have an influence that extends much further upstream and have a greater impact upon water distribution. This may contribute to observed morphological differences between sand-bedded and gravel-bedded braided river networks. Copyright © 2012 John Wiley & Sons, Ltd.

Reliable quantitative data on the extent and rates of soil erosion are needed to understand the global significance of soil-erosion induced carbon exchange and to underpin the development of science-based mitigation strategies, but large uncertainties remain. Existing estimates of agricultural soil and soil organic carbon (SOC) erosion are very divergent and span two orders of magnitude. The main objective of this study was to test the assumptions underlying existing assessments and to reduce the uncertainty associated with global estimates of agricultural soil and SOC erosion. We parameterized a simplified erosion model driven by coarse global databases using an empirical database that covers the conterminous USA. The good agreement between our model results and empirical estimates indicate that the approach presented here captures the essence of agricultural erosion at the scales of continents and that it may be used to predict the significance of erosion for the global carbon cycle and its impact on soil functions. We obtained a global soil erosion rate of 10.5 Mg ha^-1 y^-1 for cropland and 1.7 Mg ha^-1 y^-1 for pastures. This corresponds to SOC erosion rates of 193 kg C ha^-1 y^-1 for cropland and 40.4 kg C ha^-1 y^-1 for eroding pastures and results into a global flux of 20.5 (±10.3) Pg y^-1 of soil and 403.5 (±201.8) Tg C y^-1. Although it is difficult to accurately assess the uncertainty associated with our estimates of global agricultural erosion, mainly due to the lack of model testing in (sub-)tropical regions, our estimates are significantly lower than former assessments based on the extrapolation of plot experiments or global application of erosion models. Our approach has the potential to quantify the rate and spatial signature of the erosion-induced disturbance at continental and global scales: by linking our model with a global soil profile database, we estimated soil profile modifications induced by agriculture. This showed that erosion-induced changes in topsoil SOC content are significant at a global scale (an average SOC loss of 22% in 50 years) and agricultural soils should therefore be considered as dynamic systems that can change rapidly. Copyright © 2011 John Wiley & Sons, Ltd.

Hillslopes are thought to poorly record tectonic signals in threshold landscapes. Numerous previous studies of steep landscapes suggest that large changes in long-term erosion rate lead to little change in mean hillslope angle, measured at coarse resolution. New LiDAR-derived topography data enables a finer examination of threshold hillslopes. Here we quantify hillslope response to tectonic forcing in a threshold landscape. To do so, we use an extensive cosmogenic beryllium-10 (¹⁰Be)-based dataset of catchment-averaged erosion rates combined with a 500 km² LiDAR-derived 1 m digital elevation model to exploit a gradient of tectonic forcing and topographic relief in the San Gabriel Mountains, California. We also calibrate a new method of quantifying rock exposure from LiDAR-derived slope measurements using high-resolution panoramic photographs. Two distinct trends in hillslope behavior emerge: below catchment-mean slopes of 30°, modal slopes increase with mean slopes, slope distribution skewness decreases with increasing mean slope, and bedrock exposure is limited; above mean slopes of 30°, our rock exposure index increases strongly with mean slope, and the prevalence of angle-of-repose debris wedges keeps modal slopes near 37°, resulting in a positive relationship between slope distribution skewness and mean slope. We find that both mean slopes and rock exposure increase with erosion rate up to 1 mm/a, in contrast to previous work based on coarser topographic data. We also find that as erosion rates increase, the extent of the fluvial network decreases, while colluvial channels extend downstream, keeping the total drainage density similar across the range. Our results reveal important textural details lost in 10 or 30 m resolution digital elevation models of steep landscapes, and highlight the need for process-based studies of threshold hillslopes and colluvial channels. Copyright © 2012 John Wiley & Sons, Ltd.

We analyzed a combination of airborne and terrestrial LiDAR, high-resolution photography, seismic, and acoustic data in order to gain insights into the initiation, dynamics, and talus deposition of a complex rock fall. A large (46 700 m³) rock fall originated from near Ahwiyah Point in eastern Yosemite Valley and fell a total of 730 m to the valley floor on 28 March 2009. Analyses of remote sensing, seismic, and acoustic data were integrated to reconstruct the rock fall, which consisted of (1) the triggering of a 25 400 m³ rock block in an area of intersecting and sometimes highly weathered joint planes, (2) the sliding and subsequent ballistic trajectory of the block from a steeply dipping ledge, (3) dislodging of additional rock from the cliff surface from beneath the rock fall source area, (4) a mid-cliff ledge impact that detached a volume of rock nearly equivalent in volume to the initial block, (5) sliding of the deteriorating rock mass down the remainder of the cliff, and (6) final impact at the base of the cliff that remobilized the existing talus downward and outward and produced an airblast that knocked down hundreds of trees. The depositional geomorphology indicates that the porosity of the fresh talus is significantly lower than that expected for typical blocky talus slopes, likely because the rock debris from this event was pulverized into smaller, more poorly sorted fragments and densified via dynamic compaction when compared to less energetic, fragmental-type rock falls. These results suggest that accumulation of individual rock-fall boulders tends to steepen talus slopes, whereas large, energetic rock falls tend to flatten them. Detachment and impact signals were recorded by seismic and acoustic instruments and highlight the potential use of this type of instrumentation for generalized rock fall monitoring, while LiDAR and photography data were able to quantify the cliff geometry, rock fall volume, source and impact locations, and geomorphological changes to the cliff and talus. Published in 2012. This article is a US Government work and is in the public domain in the USA.

Single-thread, gravel-bed streams of moderate slope in the northern Negev are characterized by three channel units: bars exhibit steeper than average slopes and poorly sorted mixtures of small–medium cobbles and coarse–very coarse pebbles; flats are associated with more gentle slopes and well-sorted medium–fine pebbles and granules; and transitional units have intermediate slopes and grain size. In general, all three units are planar, span the full channel width and have well-defined boundaries. Bars and flats are more common than the transitional units and alternate downstream for distances of several hundred metres, forming sequences that are reminiscent of the riffle–pool structure commonly observed in humid-temperate gravel-bed rivers. A notable contrast is the absence of significant bed relief: bars lack crests and flats lack depressions. The relative lack of bed relief in bar–flat sequences is attributed to the high rate of sediment supply from the sparsely vegetated hillslopes which promotes the infilling of depressions and to the erosion of crests under conditions of intense transport. This reduction of bed relief lowers channel roughness, which in turn increases flow velocity and, therefore, the ability of the channel to transmit the large sediment loads it receives. Although our analyses pertain to a semi-arid river system, the results have wider implications for understanding the adjustment of channel bedform to high sediment loads in other fluvial environments. Copyright © 2012 John Wiley & Sons, Ltd.

The accuracy of rockfall trajectory simulations mainly rests on the calculation of the rebound of fragments following their impact on the slope. This paper is dedicated to the comparative analysis of two rebound modelling approaches currently used in rockfall simulation using field experiments of single rebounds. The two approaches consist in either modelling the rock as a single material point (lumped mass approach) or in explicitly accounting for the fragment shape (rigid body approach). A lumped mass model accounting for the coupling between translational and rotational velocities and introducing a slope perturbation angle was used. A rigid body approach modelling the rocks as rigid locally deformable (in the vicinity of the contact surface) assemblies of spheres was chosen.

The comparative analysis of the rebound models shows that both of them are efficient with only a few parameters. The main limitation of each approach are the calibration of the value of the slope perturbation (‘roughness’) angle, for the lumped mass approach, and the estimation of the rock length and height from field geological and historical analyses, for the rigid body approach. Finally, both rebound models require being improved in a pragmatic manner to better predict the rotational velocities distribution. Copyright © 2012 John Wiley & Sons, Ltd.

Progressive rock-fall failures in natural rock slopes are common in many environments, but often elude detailed quantitative documentation and analysis. Here we present high-resolution photography, video, and laser scanning data that document spatial and temporal patterns of a 15-month-long sequence of at least 14 rock falls from the Rhombus Wall, a sheeted granitic cliff in Yosemite Valley, California. The rock-fall sequence began on 26 August 2009 with a small failure at the tip of an overhanging rock slab. Several hours later, a series of five rock falls totaling 736 m³ progressed upward along a sheeting joint behind the overhanging slab. Over the next 3 weeks, audible cracking occurred on the Rhombus Wall, suggesting crack propagation, while visual monitoring revealed opening of a sheeting joint adjacent to the previous failure surface. On 14 September 2009 a 110 m³ slab detached along this sheeting joint. Additional rock falls between 30 August and 20 November 2010, totaling 187 m³, radiated outward from the initial failure area along cliff (sub)parallel sheeting joints. We suggest that these progressive failures might have been related to stress redistributions accompanying propagation of sheeting joints behind the cliff face. Mechanical analyses indicate that tensile stresses should occur perpendicular to the cliff face and open sheeting joints, and that sheeting joints should propagate parallel to a cliff face from areas of stress concentrations. The analyses also account for how sheeting joints can propagate to lengths many times greater than their depths behind cliff faces. We posit that as a region of failure spreads across a cliff face, stress concentrations along its margin will spread with it, promoting further crack propagation and rock falls. Published in 2011. This article is a US Government work and is in the public domain in the USA.

A new approach for the profiling of movable sediment beds in laboratory experiments is presented. It couples a triangulation laser sensor and an ultrasonic level transmitter, and allows a non-intrusive, fast and accurate measurement of bed topography without stopping the experimental runs. The distortion of the laser beam due to the refraction at the water surface is corrected by contemporaneously measuring the elevation of the water surface through the ultrasonic level transmitter and taking advantage of geometrical relations involving the water depth, distance of the sensors from the water surface, and the angles that the emitted laser beam forms with the vertical before and after refraction. Several tests, under either still- or flowing-water conditions, as well as increasing/decreasing water surface elevation, were carried out to evaluate the accuracy of the measurements. These tests indicate that good-quality measurements are obtained for flow depths in the range 0 < D < 60 mm, typical of morphodynamic laboratory experiments. Finally, two relevant applications to movable bed experiments carried out under either lagoonal or fluvial conditions are presented that show the effectiveness of the proposed profiling technique. Copyright © 2012 John Wiley & Sons, Ltd.

Influence of the rainfall regime on erosion and transfer of suspended sediment in a 905-km² mountainous catchment of the southern French Alps was investigated by combining sediment monitoring, rainfall data, and sediment fingerprinting (based on geochemistry and radionuclide concentrations). Suspended sediment yields were monitored between October 2007 and December 2009 in four subcatchments (22–713 km²). Automatic sediment sampling was triggered during floods to trace the sediment origin in the catchment.

Sediment exports at the river catchment outlet (330 ± 100 t km^-2 yr^-1) were mainly driven (80%) by widespread rainfall events (long duration, low intensities). In contrast, heavy, local and short duration storms, generated high peak discharges and suspended sediment concentrations in small upstream torrents. However, these upstream floods had generally not the capacity to transfer the sediment down to the catchment outlet and the bulk of this fine sediment deposited along downstream sections of the river. This study also confirmed the important contribution of black marls (up to 70%) to sediment transported in rivers, although this substrate only occupies c. 10% of the total catchment surface. Sediment exports generated by local convective storms varied significantly at both intra- and inter-flood scales, because of spatial heterogeneity of rainfall. However, black marls/marly limestones contribution remained systematically high. In contrast, widespread flood events that generate the bulk of annual sediment supply at the outlet were characterized by a more stable lithologic composition and by a larger contribution of limestones/marls, Quaternary deposits and conglomerates, which corroborates the results of a previous sediment fingerprinting study conducted on riverbed sediment. Copyright © 2012 John Wiley & Sons, Ltd.

Channel fills are common elements of Holocene river systems and older fluvial sequences, but surprisingly little is known about formation and their sedimentary build-up. Abandoned channels result from channel shifting processes at various scales, including meander cutoff and channel-belt avulsion. Channel-fill sequences are of importance as containers of palaeoenvironmental proxy-records, can be used to reconstruct palaeochannel dynamics and derive palaeoflood records, and contain materials that allow dating the abandonment. Integrated knowledge on the dynamic nature (geometrical and physical insights) of channel abandonment and resultant sedimentary recording is a necessity for comparing and collating records from a series of abandoned channel fills.

This paper intends to make channel-fill sedimentological sequences more useful recorders of channel abandonment processes and palaeofloods, for which improved understanding is needed of the internal build-up of channel fills. We review oxbow lake infilling along meandering rivers, and supplement this with highly detailed descriptions of two selected field examples of channel fills from the apex-region of the Netherlands' Rhine delta. From these examples it becomes clear that regional setting and type of abandonment result in different channel-fill end-members; oxbow cutoffs generally produce thick laminated clayey fills as the channel entrance is plugged rapidly, avulsion-abandoned channels are filled with coarse (proximal) deposits as a result of a maintained open river connection.

Field examples of channel fills are integrated with knowledge on channel abandonment dynamics in meander cutoff and bifurcating river situations, including insights from recent numerical modelling. We propose a sedimentary-architecture descriptive scheme that distinguishes elements from two stages of channel-fill development; (i) the abandonment stage with initial proximal fill, and (ii) the subsequent fully abandoned palaeochannel that collects distal fill. Copyright © 2011 John Wiley & Sons, Ltd.

Morphological features of braided rivers (bars, channels and pools) experience major changes in area, shape and spatial distribution as a response to (i) the pulsation of discharge during a flood and (ii) the bed evolution induced by floods. In this work, at-a-station relationships between water level and planform configuration were investigated on the Tagliamento River, a large gravel-bed braided river in northeast Italy, over a 2-year study period comprising three bankfull events and several small-to-medium floods. The analysis was performed on two 1-km-long reaches, characterized by different riparian vegetation cover. Ground-based images with an hourly temporal resolution were acquired using software-controlled, digital cameras. Bars, channels, pools and vegetated patches were manually digitized on more than 100 rectified images. Sequences of constant-level images spanning the study period were used to quantify the impact of floods on the stability of at-a-station relationships and on the turnover rate of water bodies.

The analysis shows that wetted area increased almost linearly with water level in both reaches. The average number of branches per cross-section peaked at intermediate flow levels, increasing from 2 at low flow up to 6–7. The number of branches displayed the largest fluctuations over time, with significant changes produced also by moderate floods. Turnover rates were high in both reaches, with more than 30% of wetted areas at low flow converting into bare gravel in less than 2 months. Vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer, deeper anabranches. The number of channels per cross-section was 30–40% less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3% to 14%. Copyright © 2011 John Wiley & Sons, Ltd.

Soil detachment in concentrated flow is due to the dislodging of soil particles from the soil matrix by surface runoff. Both aggregate stability and shear strength of the topsoil reflect the erosion resistance of soil to concentrated runoff, and are important input parameters in predicting soil detachment models. This study was conducted to develop a formula to predict soil detachment rate in concentrated flow by using the aggregate stability index (As), root density (R_d) and saturated soil strength (σ_s) in the subtropical Ultisols region of China. The detachment rates of undisturbed topsoil samples collected from eight cultivated soil plots were measured in a 3.8 m long, 0.2 m wide hydraulic flume under five different flow shear stresses (τ = 4.54, 9.38, 15.01, 17.49 and 22.54 Pa). The results indicated that the stability index (As) was well related with soil detachment rate, particularly for results obtained with high flow shear stress (22.54 Pa), and the stability index (As) has a good linear relationship with concentrated flow erodibility factors (K_c). There was a positive linear relationship between saturated soil strength (σ_s) and critical flow shear stress (τ_c) for different soils. A significant negative exponential relationship between erodibility factors (K_c) and root density (R_d) was detected. This study yielded two prediction equations that allowed comparison of their efficiency in assessing soil detachment rate in concentrated flow. The equation including the root density (R_d) may have a better correlation coefficient (R² = 0.95). It was concluded that the formula based on the stability index (As), saturated soil strength (σ_s) and root density (R_d) has the potential to improve methodology for assessing soil detachment rate in concentrated flow for the subtropical Chinese Ultisols. Copyright © 2011 John Wiley & Sons, Ltd.

The flooding susceptibility of alluvial fans in the Southern Apennines has long been neglected. To partly address this oversight, we focus on the region of Campania which contains highly urbanized piedmont areas particularly vulnerable to flooding. Our findings are based on stratigraphic analysis of the fans and morphometric analysis of the basin-fan systems. Using geomorphological analysis we recognized active alluvial fans while stratigraphic analysis together with statistical analysis of the morphometric variables was used to classify the fans in terms of the transport process involved. The results indicate that in the geological context examined, the best discrimination between debris flow (Df) and water flood (Wf) processes is achieved by means of two related variables, one for the basin (feeder channel inclination, Cg) and one for the fan (fan length, Fl). The probability that an unclassified fan belongs to group Wf is computed by applying a logistic function in which a P value exceeding 0.5 indicates that a basin/fan system belongs to group Wf. This important result led to the classification of the entire basin/fan system data. As regards process intensity, debris flow-dominated fans are susceptible to the occurrence of flows with high viscosity and hence subject to more severe events than water flood-dominated fans. Bearing this in mind, the data gathered in this study allow us to detect where alluvial fan flooding might occur and give information on the different degrees of susceptibility at a regional scale. Regrettably, urban development in recent decades has failed to take the presence of such alluvial fans into account due to the long recurrence time (50–100 years) between floods. This paper outlines the distribution of such susceptibility scenarios throughout the region, thereby constituting an initial step to implementing alluvial fan flooding control and mitigation. Copyright © 2011 John Wiley & Sons, Ltd.

Dark aeolian deposits on Mars are thought to consist of volcanic materials due to their mineral assemblages, which are common to basalts. However, the sediment source is still debated. Basaltic dunes on Earth are promising analogs for providing further insights into the assumed basaltic sand dunes on Mars. In our study we characterize basaltic dunes from the Ka'u Desert in Hawaii using optical microscopes, electron microprobe, and spectral analyses. We compare the spectra of terrestrial and Martian dune sands to determine possible origins of the Martian dark sediments. Our results show that the terrestrial sands consist primarily of medium to coarse sand-sized volcanic glass and rock fragments as well as olivine, pyroxene, and plagioclase minerals. Grain shapes range from angular to subrounded. The sample composition indicates that the material was derived from phreatomagmatic eruptions partially with additional proportions of rock fragments from local lava flows. Grain shape and size indicate the materials were transported by aeolian processes rather than by fluvial processes. Spectral analyses reveal an initial hydration of all terrestrial samples. A spectral mineralogical correlation between the terrestrial and Martian aeolian sands shows a similarity consistent with an origin from volcanic ash and lava. We suggest that the Martian deposits may contain similar abundances of volcanic glass, which has not yet been distinguished in Martian spectral data. Copyright © 2011 John Wiley & Sons, Ltd.

Comparative assessment of stone weathering intensities and bioclimatic conditions was conducted at four temples located in cleared and forested sites of the Angkor Park, based on similar protocols. Four thousand sculpted lotus petals carved in the same grey sandstone were categorized by using two customized scales of weathering intensity, and climate monitoring was conducted from December 2008 to November 2009. Whereas 70% of the sandstone lotus petals are almost completely destroyed by mechanical weathering in cleared areas, 74% of petals located in forested environments appear to be totally free of mechanical weathering and are only affected by superficial biochemical weathering. Ambient conditions are also contrasting, with the magnitude of the diurnal surface temperature and relative humidity ranges being three times higher at cleared sites than in wooded areas. As wetting–drying cycles are the driving force of sandstone decay at Angkor, causal links are suggested between weathering and climate regimes. In wooded areas, the microclimate is buffered by the forest and the associated lithobionts, which maintain constant humidity levels, reduce thermal stresses at the stone surface and induce a slow biochemical weathering regime. In cleared areas, direct exposure to sunshine and monsoon rains induces pronounced wetting–drying cycles conducive to swelling–shrinking movements and other potential processes, provoking the rapid mechanical decay of the sandstone. Even if local damage can be caused by tree roots, the forest cover and the associated lithobionts obviously play an overall protective role. Additionally, microtopographical factors related to architectural designs and post-building events probably explain intra-site and between site minor differences in the amount of sandstone decay, by influencing key factors such as the water residence time at the stone surface. Last, the contrasting weathering regimes in forested and cleared sites are but a trend, for besides overwhelming mechanical weathering, chemical weathering is also operative at cleared sites, as indicated by salt efflorescences and ferric oxidation. Copyright © 2011 John Wiley & Sons, Ltd.

In 1820, the lower Canadian River meandered through a densely forested floodplain. By 1898, most of the floodplain had been cleared for agriculture and changes in channel geometry and specific stream power followed, particularly channel widening and straightening with a lower potential specific stream power. In 1964, a large upstream hydropower dam was constructed, which changed the flow regime in the lower Canadian River and consequently the channel geometry. Without destructive overbank floods, the channel narrowed rapidly and considerably due to encroachment by floodplain vegetation. The lower Canadian River, which was once a highly dynamic floodplain-river system, has now been transformed into a relatively static river channel. These changes over the past 200 years have not been linear or independent. In this article, we use a variety of data sources to assess these historical changes along the lower Canadian River floodplain and identify feedbacks among floodplain cultivation, dam construction, specific stream power, and channel width, slope, and sinuosity. Finally, we combine the results of our study with others in the region to present a biogeomorphic response model for large Great Plains rivers that characterizes channel width changes in response to climate variability and anthropogenic disturbances. Copyright © 2011 John Wiley & Sons, Ltd.

The general nature of bulk flow within bedrock single-channel reaches has been considered by several studies recently. However, the flow structure of a bedrock-constrained, large river with a multiple channel network has not been investigated previously. The multiple channel network of the Siphandone wetlands in Laos, a section of the Mekong River, was modelled using a steady one-dimensional hydraulic model. The river network is characterized by a spatially-varying channel-form leading to significant changes in the bulk flow properties between and along the channels. The challenge to model the bulk flow in such a remote region was the lack of ideal boundary conditions. The flow models considered both low flow, high inbank and overbank flows and were calibrated using SPOT satellite sensor imagery and limited field data concerning water levels.

The application of the model highlighted flow characteristics of a large multi-channel network and also further indicated the field data that would be required to properly characterize the flow field empirically. Important results included the observation that adjacent channels within the network had different water surface slopes for the same moments in time; thus calibration data for modelling similar systems needs to account for these significant local differences. Further, the in-channel hydraulic roughness coefficient strongly varied from one cross-section to the next (Manning's ‘n’ range: 0·01 to 0·10). These differences were amplified during low flow but persisted in muted form during high discharges. Copyright © 2012 John Wiley & Sons, Ltd.

Prevailing ideas and calculations of coastal response to sea level rise (SLR) are often based on the Bruun model (Bruun P., Sea-level rise as a cause of shore erosion, Journal Waterways Harbors Division, ASCE88: 117–130, 1962) that predicts upward and landward transfer of an equilibrium profile during SLR through offshore sediment transport on the shoreface. The model is based on a number of assumptions of questionable validity as well as outdated concepts on how sediment is transported across the shoreface. This contribution takes a numerical modelling approach that is based on first-order processes contributing to the movement of sediment across the shoreface. Using a wave transformation model that predicts hydrodynamic processes driving cross-shore sediment transport and an energetics-based model for the coupling between hydrodynamics and sediment transport, we show that cross-shore sediment transport is mainly onshore directed at the boundary between the lower and the upper shoreface, in agreement with the model proposed by Davidson-Arnott (Conceptual model of the effects of sea level rise on sandy coasts, Journal of Coastal Research21: 1166–1172, 2005). The transition from onshore to offshore directed transport is located well within the surf zone and with a rising sea level this transition point becomes displaced landward and upward. Tests also show that substrate slope is of fundamental importance to the manner in which beaches react to rising sea level. Copyright © 2012 John Wiley & Sons, Ltd.

There has been limited success in determining critical thresholds of ground cover or soil characteristics that relate to significant changes in runoff or sediment production at the microscale (<1 m²), particularly in semi-arid systems where management of ground cover is critical. Despite this lack of quantified thresholds, there is an increasing research focus on the two-phase mosaic of vegetation patches and inter-patches in semi-arid systems. In order to quantify ground cover and soil related thresholds for runoff and sediment production, we used a data mining technique known as conditional inference tree analysis to determine statistically significant values of a range of measured variables that predicted average runoff, peak runoff, sediment concentration and sediment production at the microscale. On Chromic Luvisols across a range of vegetation states in semi-arid south-eastern Australia, large changes in runoff and sediment production were related to a hierarchy of different variables and thresholds, but the percentage of bare soil played a primary role in predicting runoff and sediment production in most instances. The identified thresholds match well with previous thresholds found in semi-arid and temperate regions (including the approximate values of 30%, 50% and 70% total ground cover). The analysis presented here identified the critical role of soil surface roughness, particularly where total ground cover is sparse. The analysis also provided evidence that a two-phase mosaic of patches and inter-patches identified via rapid visual assessment could be further delineated into distinct groups of hydrological response, or a multi-phase rather than a two-phase system. The approach used here may aid in assessing scale-dependent responses and address data non-linearity in studies of semi-arid hydrology. Copyright © 2012 John Wiley & Sons, Ltd.

UK peatlands are affected by severe gully erosion with consequent impacts on ecosystem services from these areas. Incision into the peat can damage the vegetation and hydrology and lead to increases in carbon loss and sediment transfer downstream. Gullies represent then a conduit for and a hotspot of carbon loss but the relatively high water tables of gullies have meant that they have been identified as areas with a high restoration potential because of easily restored peat-forming conditions. This study uses a series of gully sites, subject to different restoration interventions, to investigate differences in carbon pathways (DOC, CO₂) and hydrology between restoration strategies and gully position. The results show that the position within the gully (interfluve, gully side, or gully floor) does not significantly affect water quality but that it plays a significant role in CO₂ exchange. Gully floors are areas of high photosynthesis and ecosystem respiration, though net ecosystem exchange is not significantly different across the gully. While gully position plays a role in the cycling of some carbon species, this study highlights the importance of vegetation as a key control on carbon cycling. Copyright © 2012 John Wiley & Sons, Ltd.

The relative importance of tectonics, climate, base level and source lithology as primary factors on alluvial-fan evolution, fan morphology and sedimentary style remain in question. This study examines the role of catchment lithology on development and evolution of alluvial megafans (>30 km in length), along the flanks of the Kohrud Mountain range, NE Esfahan, central Iran. These fans toe out at axial basin river and playa-fringe sediments towards the centre of basin and tectonics, climatic change and base-level fluctuations, were consistent for their development. They formed in a tectonically active basin, under arid to semiarid climate and a long term (Plio-Pleistocene to Recent) change from wetter to drier conditions. The key differences between two of these fans, Soh and Zefreh fans, along the west and south flanks of this mountain range, is that their catchments are underlain by dissimilar bedrock types. The source-area lithologies of the Soh and Zefreh fans are in sedimentary and igneous terrains, respectively, and these fans developed their geometry mainly in response to different weathering intensities of their catchment bedrock lithologies. Fan surface mapping (based on 1/50000 topographic maps, satellite images, and fieldwork), reveals that the geomorphic evolution of these fans differs in that the relatively large-scale incision and through trenching of the Soh fan is absent in the Zefreh fan. Whereas the limited sediment supply of the Soh fan has resulted in a deep incised channel, the Zefreh fan has remained aggradational with little or no trenching into proximal to medial fan surface due to its catchment bedrock geology, composed mainly by physically weathered volcaniclastic lithology and characterized by high sediment supply for delivery during episodic flash floods. Sediment supply, which is mainly a function of climate and source lithology, is a dominant driver behind the development of fan sequences in alluvial megafans. Copyright © 2012 John Wiley & Sons, Ltd.

To quantify landscape change resulting from processes of erosion and deposition and to establish spatially distributed sediment budgets, ‘models of change’ can be established from a time series of digital elevation models (DEMs). However, resolution effects and measurement errors in DEMs may propagate to these models. This study aimed to evaluate and to modify remotely-sensed DEMs for an improved quantification of initial sediment mass changes in an artificially-created catchment. DEMs were constructed from photogrammetry-based, airborne (ALS) and ground-based laser scanning (TLS) data. Regions of differing morphological characteristics and vegetation cover were delineated. Three-dimensional (3D) models of volume change were established and mass change was derived from these models. DEMs were modified region-by-region for rill, interrill and alluvial areas, based on logical and hydro-geomorphological principles. Additional DEMs were constructed by combining multi-source, modified data. Models were evaluated by comparison with d-GPS reference data and by considering sediment budget plausibility. Comprehensive evaluation showed that DEM usability depends on a relation between the technique used to obtain elevation data, surface morphology and vegetation cover characteristics. Photogrammetry-based DEMs were suited to quantification of change in interrill areas but strongly underestimated surface lowering in erosion rills. TLS DEMs were best suited to rill areas, while ALS DEMs performed best in vegetation-covered alluvial areas. Agreement with reference data and budget plausibility were improved by modifications to photogrammetry- and TLS-based DEMs. Results suggest that artefacts in DEMs can be reduced and hydro-geomorphic surface structures can be better represented by applying region-specific modifications. Photogrammetry-based DEMs can be improved by combining higher and lower resolution data in defined structural units and applying modifications based on principles given by characteristic hydro-geomorphic evolution. Results of the critical comparative evaluation of remotely-sensed elevation data can help to better interpret DEM-based quantifications of earth-surface processes. Copyright © 2012 John Wiley & Sons, Ltd.

Predicting gully initiation at catchment scale was done previously by integrating a geographical information system (GIS) with physically based models, statistical procedures or with knowledge-based expert systems. However, the reliability and validity of applying these procedures are still questionable. In this work, a data mining (DM) procedure based on decision trees was applied to identify areas of gully initiation risk. Performance was compared with the analytic hierarchy process (AHP) expert system and with the commonly used topographic threshold (TT) technique. A spatial database was used to test the models, composed of a target variable (presence or absence of initial points) and ten independent environmental, climatic and human-induced variables. The following findings emerged: using the same input layers, DM provided better predictive ability of gully initiation points than the application of both AHP and TT. The main difference between DM and TT was the very high overestimation inherent in TT. In addition, the minimum slope observed for soil detachment was 2°, whereas in other studies it is 3°. This could be explained by soil resistance, which is substantially lower in agricultural fields, while most studies test unploughed soil. Finally, rainfall intensity events >62.2 mm h^-1 (for a period of 30 min) were found to have a significant effect on gully initiation. Copyright © 2012 John Wiley & Sons, Ltd.

The mineral magnetic properties of deposited dusts collected along a broadly north-to-south transect across Niger have been investigated on both a bulk and particle size-specific basis. Dusts display a general north-to-south gradient in fine-grained ferrimagnetic mineral (magnetite/maghemite) concentrations, with samples south of the Sahara/Sahel transition (south of ~15·5^o N) generally containing greater concentrations than dusts from further north where the climate is much drier. This distinction is seen especially clearly in the clay (< 2 µm) fraction, which harbours the products of weathering and pedogenesis. This gradient in ferrimagnetic mineral concentrations broadly parallels that previously reported for surface soils/sands across a similar latitudinal range. We suggest that the regional distinction in both dust and surface soil/sand magnetic properties can be related to differences in weathering regime between the arid Saharan parts of the transect and the Sahel sites where higher rainfall has permitted stronger weathering and pedogenesis. Given that the weathering-related magnetic signatures in the clays dominate the magnetic properties of the < 16 µm fractions in these samples, and that this particle size component is most likely to be involved in long-range transport, magnetic measurements hold out the potential of discriminating Sahara and Sahel dusts deposited in remote areas. Copyright © 2011 John Wiley & Sons, Ltd.

Quaternary period palaeoenvironmental and palaeoclimatic reconstructions are based on a wide and diverse array of proxy data sets, some of which are geomorphological in nature. In drylands, where organic proxies may be limited, the use of landforms is particularly important, but challenging. The capacity to establish the age of depositional forms, particularly through the use of luminescence dating, has advanced the use of landforms in dryland palaeo-research, though interpretation of these ‘geoproxy’ records can be complex, especially at the nexus of palaeoclimate and palaeoenvironmental interpretations of past conditions. In this paper the use of aeolian and lacustrine forms in Quaternary research is considered, focusing on the relationships between dynamics, form and climate, and on the essential linkage between process research and palaeoenvironmental research. It is concluded that landform analysis is a critical part of dryland palaeoenvironmental/climate reconstruction, contributing a different set of data compared to other data sources, in terms of the elements of past conditions that are revealed. Five principles are identified to improve the use of geoproxy records in Quaternary research: (1) greater use of geomorphic process studies by Quaternary scientists, to better inform palaeolandform interpretation; (2) further development of the use of chronometric data, especially in terms of interpreting large data; (3) interpret landform records in location-specific contexts, not in general terms; (4) capitalise of the complexity of spatially-extensive landform records, which may offer better representations of real Quaternary environmental complexity than ‘at a point’ proxies; (5) establish ways of integrating spatially-extensive geoproxy records with other palaeoenvironmental records. These challenges are major, but not insurmountable, and should represent goals for geomorphologists, chronologists and quaternary scientists alike. Copyright © 2011 John Wiley & Sons, Ltd.

Fluvial sediment transport in the high mountain Partnach River (Reintal Valley, Bavarian Alps) was investigated during a 10-year observation period (2001–2010). During this period, the downstream reach of the Partnach River was decoupled from upstream sediment throughput by a rockslide deposit until 2005. In August 2005, the dam was partially breached during a flood event resulting in renewed sediment coupling between the upstream and downstream reaches. A comparison of pre- and post-dambreak river sediment load data showed that the dissolved load dominated sediment transport prior to August 2005 with a switch to the dominance of bedload transport, post-dambreak. The higher post-dambreak bedload rates were particularly evident during the first years after the dam failure due to significant coarse material coupling between active sediment sources (undercut banks/talus cones) and the Partnach River. In the last years of the observation period (2009 and 2010) the dominance of dissolved load transport was re-established. Copyright © 2011 John Wiley & Sons, Ltd.

Meander bends of many large, sand-bed meandering rivers are partitioned by chute channels that convey permanent flow, and co-exist with the mainstem for decades. As a first step toward understanding the dynamics and morphodynamic implications of these ‘bifurcate meander bends’, this study applied binary logistic regression analysis to determine whether it is possible to predict chute initiation based on attributes of meander bend character and dynamics. Regression models developed for the Strickland River, Papua New Guinea, the lower Paraguay River, Paraguay/Argentina, and the Beni River, Bolivia, revealed that the probability of chute initiation at a meander bend is a function of the bend extension rate (the rate at which a bend elongates in a direction perpendicular to the valley axis trend). Image analyses of all rivers and field observations from the Strickland suggest that the majority of chute channels form during scroll–slough development. Rapid extension is shown to favour chute initiation by breaking the continuity of point bar deposition and vegetation encroachment at the inner bank, resulting in widely-spaced scrolls with intervening sloughs that are positively aligned with primary over-bar flow. The rivers plot in order of increasing chute activity on an empirical meandering-braided pattern continuum defined by potential specific stream power (ω_pv) and bedload calibre (D₅₀). Increasing stream power is considered to result in higher bend extension rates, with implications for chute initiation. In addition, chute stability is shown to depend on river sediment load relative to flow discharge (Qs/Q), such that while the Beni may plot in the region of highly braided rivers by virtue of a high potential specific stream power, the formation of stable chute channels is suppressed by the high sediment load. This tendency is consistent with previous experimental studies, and results in a planform that is transitional between single-thread meandering and braided. Copyright © 2011 John Wiley & Sons, Ltd.

Acquiring high resolution topographic data of natural gravel surfaces is technically demanding in locations where the bed is not exposed at low water stages. Often the most geomorphologically active surfaces are permanently submerged. Gravel beds are spatially variable and measurement of their detailed structure and particle sizes is essential for understanding the interaction of bed roughness with near-bed flow hydraulics, sediment entrainment, transport and deposition processes, as well as providing insights into the ecological responses to these processes. This paper presents patch-scale laboratory and field experiments to demonstrate that through-water terrestrial laser scanning (TLS) has the potential to provide high resolution digital elevation models of submerged gravel beds with enough detail to depict individual grains and small-scale forms. The resulting point cloud data requires correction for refraction before registration. Preliminary validation shows that patch-scale TLS through 200 mm of water introduces a mean error of less than 5 mm under ideal conditions. Point precision is not adversely affected by the water column. The resulting DEMs can be embedded seamlessly within larger sub-aerial reach-scale surveys and can be acquired alongside flow measurements to examine the effects of three-dimensional surface geometry on turbulent flow fields and their interaction with instream ecology dynamics. Copyright © 2011 John Wiley & Sons, Ltd.

Rain splash erosion is an important soil transport mechanism on steep hillslopes. The rain splash process is highly stochastic; here we seek to constrain the probability distribution of splash transport distances on natural hillslopes as a function of hillslope gradient and total precipitation depth. Field experiments were conducted under natural precipitation events to observe splash travel on varying slope gradients. The downslope fraction of splash transport on 15°, 25° and 33° gradients were 85%, 96% and 96%, respectively. Maximum splash transport (L_max) was related to the rain splash detachment of soil particles and slope gradient. An empirical relationship of L_max to the precipitation depth and gradient was obtained; it is linearly proportional to hillslope gradient and logarithmically related to precipitation depth. Measured splash distances were calibrated to the fully two-dimensional (2D) model of splash transport of Furbish et al. (Journal of Geophysical Research112: F01001, 2007) that is based on the assumption that radial splash distances are exponentially distributed; calibrated values of mean splash transport distances are an order of magnitude greater than those previously determined in a controlled laboratory setting. We also compared measured data with several one-dimensional (1D) probability distributions to asses if splash transport distances could be better explained by a heavy-tailed probability distribution rather than an exponential probability distribution. We find that for hillslopes of 15° and 25°, although a log-normal probability distribution best describes the data, we find its likelihood is nearly indistinguishable from an exponential distribution based on computing maximum likelihood estimators for all 1D distributions (exponential, log-normal and Weibull). At 33°, however, we find stronger evidence that measured travel distances are heavy-tailed. Copyright © 2011 John Wiley & Sons, Ltd.

Historical, human-induced channel adjustments in lowland gravel-bed rivers have been documented in several geographical contexts worldwide. In particular, it is now widely accepted that the vast majority of European rivers are far from any natural, reference state prior to anthropic disturbances, and a ‘complete’ restoration is hardly achievable. However, few investigations have addressed changes that have occurred in mountain rivers of the Alps, and these channels are commonly reckoned quite ‘natural’ by society. This paper intends to describe how human pressure on Italian Alpine basins has been quite relevant for several centuries – in terms of land-use variations, in-channel structures, timber transport (splash damming) and riparian vegetation management – such that nowadays ‘reference conditions’ cannot be found even in small mountain creeks. In addition, recent natural climatic variations (e.g. the Little Ice Age) are superimposed on human disturbances, thus defying the definition of any ‘equilibrium’ morphological conditions even under ‘human-free’ states. A summary of published as well as unpublished works on historical channel adjustments in rivers of the Italian Alps is presented in order to document the impacts deriving from human pressure at different basin scales and for different river morphologies, from steep confined streams to large unconfined rivers. General options for river management and restoration actions aiming to combine geomorphological functionality and flood hazard mitigation are discussed, in the light of the current European legislative context. Copyright © 2011 John Wiley & Sons, Ltd.

Landscape-scale variation in rock fragments on soil-mantled hillslopes is poorly understood, despite the potential importance of rock fragments in soil weathering and coarse sediment supply to river networks. We explored the utility of soil survey databases for data mining, with the goals of identifying landscape-scale patterns in the abundance and size distribution of rock fragments (diameter D > 2 mm) and potential controls on grain size production. We focus on data from three regions: the Hawaiian Islands, and the Sierra Nevada and Cascade Mountains, where elevation transects span a range of environmental conditions. We selected pedons from pits dug on hillslopes with active soil production and transport. For the 27 pedons selected, we constructed depth-averaged grain size distributions and calculated the mass fraction of rock fragments (F_RF) and the median rock fragment grain size (D_50RF). We also categorized as bimodal, size distributions with a clear ‘breakpoint’ between fine and coarse modes. Several strong patterns emerge from the data. We find rock fragments in 85% of the pedons, primarily in distinct coarse modes within bimodal size distributions. Values of F_RF and D_50RF are strongly correlated, although the best-fit power law scaling between F_RF and D_50RF differs between the warmer Hawaiian, and colder Sierra Nevada and Cascade Mountain sites. We also find a regional contrast in the variation in F_RF with elevation; F_RF declines with elevation in Hawaii, but increases in the mainland sites. Although this contrast could be an artifact of variable lithology, precipitation may influence many patterns in the data. Lower mean-annual precipitation correlates with higher F_RF, dominantly bimodal distributions and surface enrichment in the vertical distribution of rock fragments. These observations may be useful in refining models of coarse sediment supply to rivers, and suggest opportunities for future work to test mechanistic hypotheses for rock fragment production on soil-mantled hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.

This study analyses beach morphological change during six consecutive storms acting on the meso-tidal Faro Beach (south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub-aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run-up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep-sloping beaches, since sub-aerial beach volume reductions up to 30 m³/m were followed by intertidal area recovery (–2 < z < 3 m) with rates reaching ~10 m³/m. However, the observed cumulative dune erosion and profile pivoting imply that storms, even of regular intensity, can have a dramatic impact when they occur in groups. Nearshore bars seemed to respond to temporal scales more related to storm sequences than to individual events. The formation of a prominent crescentic offshore bar at ~200 m from the shoreline appeared to reverse the previous offshore migration trend of the inner bar, which was gradually shifted close to the seaward swash zone boundary. The partially understood nearshore bar processes appeared to be critical for storm wave attenuation in the surf zone; and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of standard, non-dimensional, morphological parameters. Copyright © 2011 John Wiley & Sons, Ltd.

This study developed and evaluated a hybrid approach to remote measurement of river morphology that combines LiDAR topography with spectrally based bathymetry. Comparison of filtered LiDAR point clouds with surveyed cross-sections indicated that subtle features on low-relief floodplains were accurately resolved by LiDAR but that submerged areas could not be detected due to strong absorption of near-infrared laser pulses by water. The reduced number of returns made the active channel evident in a LiDAR point density map. A second dataset suggested that pulse intensity also could be used to discriminate land from water via a threshold-based masking procedure. Fusion of LiDAR and optical data required accurate co-registration of images to the LiDAR, and we developed an object-oriented procedure for achieving this alignment. Information on flow depths was derived by correlating pixel values with field measurements of depth. Highly turbid conditions dictated a positive relation between green band radiance and flow depth and contributed to under-prediction of pool depths. Water surface elevations extracted from the LiDAR along the water's edge were used to produce a continuous water surface that preserved along-channel variations in slope. Subtracting local flow depths from this surface yielded estimates of the bed elevation that were then combined with LiDAR topography for exposed areas to create a composite representation of the riverine terrain. The accuracy of this terrain model was assessed via comparison with detailed field surveys. A map of elevation residuals showed that the greatest errors were associated with underestimation of pool depths and failure to capture cross-stream differences in water surface elevation. Nevertheless, fusion of LiDAR and passive optical image data provided an efficient means of characterizing river morphology that would not have been possible if either dataset had been used in isolation. Copyright © 2011 John Wiley & Sons, Ltd.

We evaluate the validity of the beaver-meadow complex hypothesis, used to explain the deposition of extensive fine sediment in broad, low-gradient valleys. Previous work establishes that beaver damming forms wet meadows with multi-thread channels and enhanced sediment storage, but the long-term geomorphic effects of beaver are unclear. We focus on two low-gradient broad valleys, Beaver Meadows and Moraine Park, in Rocky Mountain National Park (Colorado, USA). Both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes. We examine the geomorphic significance of beaver-pond sediment by determining the rates and types of sedimentation since the middle Holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition. Sediment analyses from cores and cutbanks indicate that 33–50% of the alluvial sediment in Beaver Meadows is ponded and 28–40% was deposited in-channel; in Moraine Park 32–41% is ponded sediment and 40–52% was deposited in-channel. Radiocarbon ages spanning 4300 years indicate long-term aggradation rates of ~0.05 cm yr^-1. The observed highly variable short-term rates indicate temporal heterogeneity in aggradation, which in turn reflects spatial heterogeneity in processes at any point in time. Channel complexity increases directly downstream of beaver dams. The increased complexity forms a positive feedback for beaver-induced sedimentation; the multi-thread channel increases potential channel length for further damming, which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped. Channel complexity decreased significantly as surveyed beaver population decreased. Beaver Meadows and Moraine Park represent settings where beaver substantially influence post-glacial floodplain aggradation. These findings underscore the importance of understanding the historical range of variability of valley bottom processes, and implications for environmental restoration. Copyright © 2011 John Wiley & Sons, Ltd.

The development of cavernous weathering features such as tafoni remains poorly understood. In particular, the roles played by internal moisture and case hardening remain unclear. In this study, Electric Resistivity Tomography (ERT) has been used to map moisture distribution within inner walls of tafoni developed in sandstone, and an Equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening. Seven large tafoni in the Golden Gate Highlands National Park (South Africa), varying in size and degree of development have been monitored. A dynamic relationship between surface hardness, degree of weathering and internal moisture regimes has been found. We propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research. Copyright © 2011 John Wiley & Sons, Ltd.

A progression of induration, erosion, and redeposition of transverse and networked transverse aeolian ridges (TARs) has been documented in the Medusae Fossae Formation (MFF), Mars. Cratered and eroded aeolian bedforms are rarely observed on Mars, indicating that those found in the MFF have been inactive for much longer than those found elsewhere. Indurated TARs are observed to grade into faceted MFF terrain, indicating a genetic relationship between the two. We propose that TAR deposition, induration and erosion have played a larger role in the surface morphology and evolution of the MFF than previously recognized. The deposition, induration, and erosion of TARs indicate that the MFF has undergone multiple cycles of reworking, and that much of its current surface morphology does not reflect the circumstances of its primary emplacement. Copyright © 2011 John Wiley & Sons, Ltd.

In the first decades of the 20th century, the Ebro River was the Iberian channel with the most active fluvial dynamics and the most remarkable spatial-temporal evolution. Its meandering typology, the dimensions of its floodplain, and the singularities of its flow regime produced an especially interesting set of river functions.

The largest dynamics of the Ebro River are concentrated along the meandering profile of the central sector. During the 20th century, this sector experienced a large alteration of its geomorphological structure. We present here an analysis of this evolution through the cartographic study of a long segment of the river (~250 km) in 1927, 1956 and 2003. The results show a large reduction in bank sinuosity, a progressive loss of fluvial territory, and a large decrease in channel width. These changes are especially clear in the areas previously most ecologically connected with the active channel. The fluvial territory of the river in 2003 was approximately half that found during the first decades of the 20th century. Forest plantations, which were non-existent in 1927, occupied more than 1500 ha of the study area in the last decade.

This intense geomorphological transformation becomes ecologically visible in (i) a 35% reduction of the area occupied by riparian vegetation; (ii) a loss of the heterogeneity of riparian forest spots, which were formerly structured in an irregular mosaic far from the river thalweg; and (iii) a modification of the riparian forest structure, which is currently linear, uniform, thin and very close to the river axis. The ecomorphological alteration was intensified by the remarkable reduction in bank length (13%) and the reduced dynamism of the present river system, indicated by an increase in the percentage of fluvial territory occupied by riparian forests and a reduction in the area occupied by the active channel. Copyright © 2002 John Wiley & Sons, Ltd.

Low-elevation areas within a sandy barrier island are subject to flooding via saturation overland flow following moderate storm surges and rainfall events. Using a high resolution topographic survey and simple hydrology models, we estimate the discharge and velocities from storm surge return flow and saturation overland flow. Results show that return flow velocities are of the same magnitude as the critical velocity necessary to mobilize sand when a hydraulic connection between the watershed and back-barrier bay is present. Storms of moderate strength and rainfall intensity may be sufficient to keep the return channels open within the back-barrier, thus providing natural conduits for water exchange from overwash events during extreme storm surges triggered by hurricanes. Copyright © 2011 John Wiley & Sons, Ltd.

Data are reported demonstrating the potential role of microscale morphologies, induced by endolithic lichen communities, specifically Verrucaria baldensis, in the initiation and development of mesoscale solution basin formation on limestone in the Burren, County Clare. A biophysical model is proposed outlining the different microscale stages leading to solution basin initiation with a progression from initial lichen colonization and growth, associated perithecial biopitting followed by biopit coalescence to form biotroughs, their subsequent enlargement and eventual incipient solution basin formation. This model provides one explanation for solution basin development as this end state may also be achieved through simple solutional means without biological input. The complexity of interactions at the lichen–rock interface are identified with emphasis on the spatial and temporal variability of these underlining the point that, as with macrotopographies at the landscape scale, rock surface microtopographies also reflect historical weathering legacies. Copyright © 2011 John Wiley & Sons, Ltd.

Studies of soil erosion on small plots present upscaling problems. The results in the literature on the effect of slope length (i.e. scale) on runoff and soil erosion are contradictory. Furthermore, most studies that examine scale effects measured through erosion plots have been conducted in Mediterranean environments. The objective of this study was to assess the effects of plot size on runoff and soil loss in a subtropical environment. Other measurements were taken to appraise the topsoil property changes inside the plots. The soil was ploughed twice, the surface was leveled with a hoe and it was kept bare during the experiment. Data were collected from 10 paired plots, five plots measuring 10 m × 1 m and five plots measuring 1 m × 1 m, installed in the same pedo-geomorphologic unit. Measurements were carried out from November 2008 to November 2009. During this period, 97 natural storms were registered. The results indicate that the small plots tended to have higher runoff (30% higher) compared to larger plots, especially during periods of greater rainfall volume, duration and intensity. The soil loss was similar in both the 1 m² plots (6·33 kg/m²) and the 10 m² plots (6·26 kg/m²). Moreover, the dynamics of the soil loss during the experiment was relatively similar across both plot sizes. The large plots tended to have a greater internal complexity. In these plots, the steps retreat were higher, the overland flow scars were more frequent, and points of rill initiation and protochannels emerged in several parts of the plots. The results of the small plots were comparable to the results obtained on the large plots, especially in relation to soil loss. These plots were useful for short-term assessments of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.

This paper reports a radiofrequency identification (RFID) tracing experiment implemented in a high-sediment-load mountain stream typical of alpine gravel-bed torrents. The study site is the Bouinenc Torrent, a tributary to the Bléone River in southeast France that drains a 38·9-km² degraded catchment. In spring 2008, we deployed 451 tracers with b-axis ranging from 23 to 520 mm. Tracers were seeded along eight cross-sections located in the upstream part of the lowest 2·3 km of the stream. Three tracer inventories were implemented in July 2008, 2009 and 2010. Recovery rates calculated for mobile tracers declined from 78% in 2008 to 45% in 2009 and 25% in 2010. Observations of tracer displacement revealed very high sediment dispersion, with frontrunners having travelled more than 2 km only three months after their deployment. The declining recovery rate over time was interpreted as resulting from rapid dispersion rather than deep burial. We evaluated that 64% of the tracers deployed in the active channel were exported from the 2·3-km study reach three years after the onset of the tracing experiment. Travel distances were characterized by right-skewed and heavy-tailed distributions, correctly fitted by a power-law function. This supports the idea that in gravel-bed rivers with abundant sediment supply relative to transport capacity, bedload transport can be viewed as a superdiffusive sediment dispersion process. It is also shown that tracers initially deployed in the low-flow channel were characterized by a 15- to 30-fold increase of mobility compared to tracers deployed in gravel bars. Copyright © 2011 John Wiley & Sons, Ltd.

The Australian Nullarbor Plain, one of the world's largest limestone platforms (~200 000 km²), has few distinctive surface karst features for its size, but is known for its enigmatic ‘blowholes’, which can display strong barometric draughts. Thousands of these vertical tubes with decimetre–metre (dm–m) scale diameter puncture the largely featureless terrain. The cause and distribution of these has remained unclear, but they have been thought to originate from downward dissolution and/or salt weathering.

To elucidate blowhole distribution and mode of formation we (i) correlated existing location data with Shuttle Radar Topography Mission (SRTM) data, which distinguishes the subtle undulations (< 10 m per km) of the landscape, (ii) surveyed blowhole morphology and (iii) determined their rock surface hardness.

Over a sampled area of 4200 km², the distribution of 615 known blowholes is not correlated with present topography. Blowholes are often connected to small or, in some cases extensive, but typically shallow cavities, which exhibit numerous ‘cupolas’ (dome-shaped pockets) in their ceilings. Statistical arguments suggest that cavities with cupolas are common, but in only a few cases do these puncture the surface. Hardness measurements indicate that salt weathering is not their main cause. Our observations suggest that blowholes do not develop downwards, but occur where a cupola breaks through the surface. Lowering of the land surface is suggested to be the main cause for this breakthrough. Although cupolas may undergo some modification under the current climate, they, as well as the shallow caves they are formed in, are likely to be palaeokarst features formed under a shallower water table and wetter conditions in the past. The findings presented have implications for theories of dissolutional forms development in caves worldwide. The environmental history of the Nullarbor platform allows testing of such theories, because many other factors, which complicate karst evolution elsewhere, have not interfered with landform evolution here. Copyright © 2011 John Wiley & Sons, Ltd.

The paper presents the results of a multi-temporal, differential interferometric synthetic aperture radar (DInSAR) analysis aiming to identify active surface deformation phenomena in south-eastern Sicily. The study area has been chosen because of its strong seismicity, high concentration of industrial and agricultural activities, and high density of people living in the coastal area. Furthermore, the morphology, lithology and climatic features of this sector of the Hyblean foreland are suitable for an interferometric analysis, providing a high coherence over the area. The Small BAseline Subset (SBAS) multitemporal DInSAR technique was used to calculate mean ground velocity maps and displacement time series from a large data set of European Remote Sensing Satellites (ERS 1–2) images spanning the time period 1992–2000. The reliability of the DInSAR results was tested calculating the East_SAR and Up_SAR values over two permanent global positioning system (GPS) stations in the area, and comparing them with the East_GPS and Up_GPS values. The residuals between GPS and DInSAR velocities were 1 and 0.6 mm/yr for the Up and East components, respectively. Four main subsiding areas, previously undetected, have been identified, corresponding with the towns of Augusta, Siracusa, Priolo, and Villasmundo. The observed deformation phenomena are located within coastal structural basins, filled with Pleistocene and Holocence deposits, except the Villasmundo land subsidence, which is located on the Hyblean plateau. The measured deformation rates reach values up to −18 mm/yr in Augusta, –6 mm/yr in Siracusa, –5 mm/yr in Villasmundo and −4.5 mm/yr in Priolo. The examination of velocity profiles, time series, and geological data allows us to relate all the detected deformation patterns primarily to groundwater over-exploitation. A multi-dimensional interpolation with kriging was performed to obtain a field subsidence map. A first-order elastic deformation model was used to simulate the peculiar features of the Villasmundo subsidence. Copyright © 2011 John Wiley & Sons, Ltd.

Remote mapping and measurement of surface processes at high spatial resolution is among the frontiers in Earth surface process research. Remote measurements that allow meter-scale mapping of landforms and quantification of landscape change can revolutionize the study of landscape evolution on human timescales. At Mill Gulch in northern California, USA, an active earthflow was surveyed in 2003 and 2007 by airborne laser swath mapping (ALSM), enabling meter-scale quantification of landscape change. We calculate four-year volumetric flux from the earthflow and compare it to long-term catchment average erosion rates from cosmogenic radionuclide inventories from adjacent watersheds. We also present detailed maps of changing features on the earthflow, from which we can derive velocity estimates and infer dominant process. These measurements rely on proper digital elevation model (DEM) generation and a simple surface-matching technique to align the multitemporal data in a manner that eliminates systematic error in either dataset. The mean surface elevation of the earthflow and an opposite slope that was directly influenced by the earthflow decreased 14 ± 1 mm/yr from 2003 to 2007. By making the conservative assumption that these features were the dominant contributor of sediment flux from the entire Mill Gulch drainage basin during this time interval, we calculate a minimum catchment-averaged erosion rate of 0·30 ± 0·02 mm/yr. Analysis of beryllium-10 (¹⁰Be) concentrations in fluvial sand from nearby Russian Gulch and the South Fork Gualala River provide catchment averaged erosion rates of 0·21 ± 0·04 and 0·23 ± 0·03 mm/yr respectively. From translated landscape features, we can infer surface velocities ranging from 0·5 m/yr in the wide upper ‘source’ portion of the flow to 5 m/yr in the narrow middle ‘transport’ portion of the flow. This study re-affirms the importance of mass wasting processes in the sediment budgets of uplifting weak lithologies. Copyright © 2011 John Wiley & Sons, Ltd.

Understanding fluvial adjustments to base level changes benefits the fields of sequence stratigraphy, geomorphology and petroleum geology. This investigation is a modern case study of the channel dynamics of Lee Creek and the Goggin Drain, two streams that are part of the Jordan River drainage into the endorheic Great Salt Lake of northern Utah, a lacustrine system that has experienced multiple, decadal-scale base level changes. Since 1965, the lake level has fluctuated in elevation more than 6 m, transitioning from an historic lowstand [< 1279 m above sea level (a.s.l.)] to an historic highstand (>1284 m a.s.l.), and in 2009–2010 approaching an historic lowstand. This study uses detailed aerial images, fieldwork and LiDAR data to link the modern geomorphology and channel hydraulics to specific variations in sediment transport, channel form, and avulsion behavior. Although Lee Creek and the Goggin Drain are situated only a few kilometers apart and share similar shore zone gradients, substrates and vegetation patterns, and have been subjected to the same changes in lake level, their channel forms have evolved very differently. Differences in discharge patterns are likely the most influential factor causing the meandering form of Lee Creek and the braiding channel of the Goggin Drain. Despite the differences in discharge, total sediment eroded from the two streams is comparable and can be attributed to similar stream power/unit stream width in the two streams. Although Lee Creek has not recently been avulsive, three major avulsions of the Goggin Drain have taken place since 1965. Two possible styles of avulsion are interpreted: an allogenic response to changing base level, and an autogenic response dictated by channel morphology and hydraulics. Despite a wealth of available information, avulsions cannot be unequivocally attributed to one style or another. Caution should be used when attempting to link the complex process of avulsion to causal mechanisms. Copyright © 2011 John Wiley & Sons, Ltd.

Concentrated flow is often the dominant source of water erosion following disturbance on rangelands. Because of the lack of studies that explain the hydraulics of concentrated flow on rangelands, cropland-based equations have typically been used for rangeland hydrology and erosion modeling, leading to less accurate predictions due to different soil and vegetation cover characteristics. This study investigates the hydraulics of concentrated flow using unconfined field experimental data over diverse rangeland landscapes within the Great Basin Region, United States. The results imply that the overall hydraulics of concentrated flow on rangelands differ significantly from those of cropland rills. Concentrated flow hydraulics on rangelands are largely controlled by the amount of cover or bare soil and hillslope angle. New predictive equations for concentrated flow velocity (R² = 0·47), hydraulic friction (R² = 0·52), and width (R² = 0·4) representing a diverse set of rangeland environments were developed. The resulting equations are applicable across a wide span of ecological sites, soils, slopes, and vegetation and ground cover conditions and can be used by physically-based rangeland hydrology and erosion models to estimate rangeland concentrated flow hydraulic parameters. Published in 2011. This article is a US Government work and is in the public domain in the USA.

In this study, we proposed a new approach for linking event sediment sources to downstream sediment transport in a watershed in central New York. This approach is based on a new concept of spatial scale, sub-watershed area (SWA), defined as a sub-watershed within which all eroded soils are transported out without deposition during a hydrological event. Using (rainfall) event data collected between July and November, 2007 from several SWAs of the studied watershed, we developed an empirical equation that has one independent variable, mean SWA slope. This equation was then used to determine event-averaged unit soil erosion rate, Q_S/A, (in kg/km²/hr) for all SWAs in the studied watershed and calculate event-averaged gross erosion E_ea (in kg/hr). The event gross erosion E_t (in kilograms) was subsequently computed as the product of E_ea and the mean event duration, T (in hours) determined using event hydrographs at the outlet of the studied watershed. Next, we developed two linear sediment rating curves (SRCs) for small and big events based on the event data obtained at the watershed outlet. These SRCs, together with T, allowed us to determine event sediment yield SY_e (in kilograms) for all events during the study period. By comparing E_t with SY_e, developing empirical equations (i) between E_t and SY_e and (ii) for event sediment delivery ratio, respectively, we revealed the event dynamic processes connecting sediment sources and downstream sediment transport. During small events, sediment transport in streams was at capacity and dominated by the deposition process, whereas during big events, it was below capacity and controlled by the erosion process. The key of applying this approach to other watersheds is establishing their empirical equations for Q_S/A and appropriately determining their numbers of SWAs. Copyright © 2011 John Wiley & Sons, Ltd.

Dryland rivers are recognized for limited research and high uncertainties with respect to understanding biogeomorphic processes. This study uses aerial photography, sediment analysis, palynology indicators and hydraulic modelling to investigate the role of riparian vegetation in influencing the response of systems to disturbance, the trajectory of channel evolution and the potential for management. The study focuses on cleared and uncleared sites in the Yerritup catchment, along the south coast of Western Australia, that occur along a transect with a consistent stream gradient and landscape topographic setting.

Downstream reaches show no gross botanical change, but gradual sediment deposition across the floodplain of up to 40 cm based on palynological and sedimentary indicators. Channel response in the cleared section by incision, widening and floodplain degradation began rapidly after land clearing, but is driven by large flood events. Degradation of riparian vegetation has significantly increased the sensitivity of the system. The cleared reaches have transformed from a low-capacity channel, under-adjusted to the prevailing flow regime, to the large present channel that is now over-adjusted to the predominantly low to moderate seasonal (occasional flood) flow regime. Modelling of pre-settlement erosive potential reveals that the entire system was naturally sensitive to change, and was primed to erode once riparian vegetation was removed.

The trajectory of channel evolution and the role of riparian vegetation is examined in relation to undisturbed reaches in the system and an appreciation of the historical range of variability in geomorphic response. Analysis of the patterns of contemporary vegetation growth identify the potential to re-establish vegetation where it is elevated from saline baseflow. However, the system is assessed as being close to a threshold where restoration is no longer possible and remediation options become more limited as eco-hydraulic and hydrochemical changes continue. Copyright © 2011 John Wiley & Sons, Ltd.

Soil redistribution on arable land significantly affects lateral and vertical soil carbon (C) fluxes (caused by C formation and mineralization) and soil organic carbon (SOC) stocks. Whether this serves as a (C) sink or source to the atmosphere is a controversial issue. In this study, the SPEROS-C model was modified to analyse erosion induced lateral and vertical soil C fluxes and their effects upon SOC stocks in a small agricultural catchment (4·2 ha). The model was applied for the period between 1950 and 2007 covering 30 years of conventional tillage (1950–1979) followed by 28 years of conservation tillage (1980–2007). In general, modelled and measured SOC stocks are in good agreement for three observed soil layers. The overall balance (1950–2007) of erosion induced lateral and vertical C fluxes results in a C loss of −4·4 g C m^–2 a^–1 at our test site. Land management has a significant impact on the erosion induced C fluxes, leading to a predominance of lateral C export under conventional and of vertical C exchange between soil and atmosphere under conservation agriculture. Overall, the application of the soil conservation practices, with enhanced C inputs by cover crops and decreased erosion, significantly reduced the modelled erosion induced C loss of the test site. Increasing C inputs alone, without a reduction of erosion rates, did not result in a reduction of erosion induced C losses. Moreover, our results show that the potential erosion induced C loss is very sensitive to the representation of erosion rates (long-term steady state versus event driven). A first estimate suggests that C losses are very sensitive to magnitude and frequency of erosion events. If long-term averages are dominated by large magnitude events modelled erosion induced C losses in the catchment were significantly reduced. Copyright © 2011 John Wiley & Sons, Ltd.

Evaluation of historic range of variability (HRV) is an effective tool for determining baseline conditions and providing context to researchers and land managers seeking to understand and enhance ecological function. Incorporating HRV into restoration planning acknowledges the dynamic quality of landscapes by allowing variability and disturbance at reasonable levels and permitting riverine landscapes to adapt to the physical processes of their watersheds. HRV analysis therefore represents a practical (though under-utilized) method for quantifying process-based restoration goals. We investigated HRV of aggradational processes in the subalpine Lulu City wetland in Rocky Mountain National Park to understand the impacts of two centuries of altered land use and to guide restoration planning following a human-caused debris flow in 2003 that deposited up to 1 m of sand and gravel in the wetland. Historic aerial photograph interpretation, ground penetrating radar surveys, and trenching, coring, and radiocarbon dating of valley-bottom sediments were used to map sediment deposits, quantify aggradation rates, and identify processes (in-channel and overbank fluvial deposition, direct hillslope input, beaver pond filling, peat accumulation) creating alluvial fill within the wetland. Results indicate (i) the Lulu City wetland has been aggrading for several millennia, (ii) the aggradation rate of the past one to two centuries is approximately six times higher than long-term pre-settlement averages, (iii) during geomorphically active periods, short-term aggradation rates during the pre-settlement period were probably much higher than the long-term average rate, and (iv) the processes of aggradation during the last two centuries are the same as historic processes of aggradation. Understanding the HRV of aggradation rates and processes can constrain management and restoration scenarios by quantifying the range of disturbance from which a landscape can recover without active restoration. Copyright © 2011 John Wiley & Sons, Ltd.

Studies on pool morphologies include reports of over 80% or 90% of pools being associated with structural controls and large obstructions that include boulders, bedrock outcrops and large woody debris (LWD). A Monte Carlo simulation approach and developmental computer model was created to predict pool formation, spacing and the percentage length covered by pools, riffles, scour holes and runs based on input data that include channel slope, width, the number of small and large boulders, and the number of 10–30 cm, 30–60 cm and >60 cm pieces of wood. The statistical-empirical model is founded on the idea that boulders, bedrock outcrops and large woody debris provide a physical framework that then controls local water-surface slopes, velocity patterns and the locations of pools and riffles. The spacing values of individual types and sizes of obstructions are modeled as log-normal distributions with separate distributions for each obstruction type. Pools are assigned different probabilities of development depending on the obstruction type. Pool and riffle lengths used to create the subsequent morphology follow their own slope-dependent, log-normal trends. A minimum distance develops between successive pools because of the backwater and turbulent conditions needed for pool formation. The total number and spacing of pools, riffles and scour holes thus reflects the number and locations of obstructions and characteristics of the pool–riffle couplet. The simulation model accurately captures the number of pools in the modeled data range at 65% of all the verification field sites, and 86% of the verification field sites with a more limited range of width and slope characteristics. Lower levels of prediction capabilities are associated with modeled numbers of scour holes and log jams. The model accurately mimics some statistical attributes of pool spacing, and future versions of the model could be developed to improve overall predictive capabilities. Copyright © 2011 John Wiley & Sons, Ltd.

Field investigations that help clarify local sedimentary processes involved in the migration of alternate bars as a consequence of flood events are lacking. A simple approach combining scour chains, stratigraphy and frequent bathymetric surveys is proposed to connect the dynamics of free migrating alternate bars present in disconnected channels of large sandy-gravelly rivers with their sedimentary products and vice versa. The results show that the spatial distribution of bars before a flood partly governs the scour and fill processes and that the sediment transport rates vary significantly on a single cross-section. This can be due to preferential axes of the migration of the bars determined by their location on the cross-section, the bank direction and the discharge. The approach allows the reconstruction of local sedimentary processes involved in alternate bar migration by combining maximum scour depths reached during a flood with frequent channel bed topography surveys and post-flood stratigraphy. It is also possible to distinguish deposited and preserved sediments compared with sediments by-passed during the flood. Copyright © 2011 John Wiley & Sons, Ltd.